Project 1. Molecular mechanism of adenovirus-mediated induction and shut-off of DHFR gene expression. Infection of methotrexate-resistant cells containing amplified genes coding for dihydrofolate reductase (DHFR) with human adenoviruses results in the induction and subsequent shut-off of DHFR-specific mRNA biosynthesis (1). Both induction and shut-off are mediated by nuclear events culminating in alterations in the rate of appearance of newly-synthesized DHFR-specific mRNA sequences in the cytoplasm. Part 1 of this proposal describes experiments investigating the molecular mechanism of induction and shut-off. This will include kinetic and structural investigations of DHFR-specific transcripts. Project 2. The role of viral gene products in induction and shut-off of DHFR gene expression. Viral E1A gene products are implicated as important in induction of host functions, induction of viral functions, and viral transformation. Investigations into the second of these processes suggests that E1A products act by transcriptional alterations. The molecular mechanism whereby the multiple products of the E1A region affect the expression of DHFR will be investigated through the use of mutants or conditions which alter the production of E1A products. These experiments should better define the role of ElA products in both productive infections and transformation. Expression of cellular genes involved in housekeeping functions such as DHFR can be induced by a variety of perturbations including virus infection, transformation, and progression through the cell cycle. The transcriptional mechanisms operating to control DHFR-specific RNA production during productive infection, non-productive infection, transformation, and growth regulation will be examined and compared to determine if these diverse events trigger common or different transcriptional regulatory pathways.